Electrode for television tubes



June 11, 1940. R 5 JAMES 2,204,251

ELECTRODE FOR TELEVISION TUBES Filed Sept. 29, 1937' INVENTOR. 5ER7' B. JANES ATTORNEY.

Patented June 11, 1940 UNITED STATES PATENT OFFICE ELECTRODE FOR TELEVISION TUBES Delaware Application September 29, 1937, Serial No. 166,250

1 Claim.

My invention realtes to multi-apertured electrodes of the mosaic type, such as are used in television transmitting and receiving tubes.

Many types of television transmittingor receiving tubes such as shown in U. S. Patent 2,047,369, July 14, 1936 to W. H. Hickok, utilize a double-sided mosaic electrode which consists in general of a fine mesh foundation screen of electrically conducting wire coated with a vitreous insulating enamel, the interstices of the mesh being filled with electrically conducting silver plugs which are oxidized and treated with caesium to provide surfaces high in photoelectric emission or surfaces having high secondary electron emission when bombarded by a beam of high velocity electrons. It has been found necessary in such electrodes to use an insulating enamel of very high leakage resistance, and that the silver tends to diffuse into the conventional vitreous enamels during the manufacturing process and during use, resulting in high electrical leakage between the silver plugs and the mesh foundation.

It is an object of my. invention to provide a double-sided mosaic electrode for use in television transmitting and receiving tubes wherein the electrical leakage between the metal plugs and the foundation is a minimum. Another object of my invention isto provide a doublesided mosaic type electrode having minimum leakage and high photoelectron emissivity. It is a further object of my invention to provide a double-sided mosaic electrode having over its entire surface a higher and more uniform elec- 5 trical resistance than such electrodes as heretofore made. It is a still further object of my invention to provide a simple and convenient method of manufacturing such a double-sided mosaic electrode.

In accordance with my invention leakage between the. individual metal plugs and the foundation member of the mosaic electrode is minimized by using for the plugs a metal which is substantially insoluble in the vitreous enamel on the foundation. Further, in accordance with the invention, a mosaic electrode with plugs of a metal which will not diffuse into the insulating material may have the metal plugs coated on their exposed surfaces with another metal which when oxidized and treated with caesium or other alkali metal provides surfaces having high photoemissivity or high secondary electron emissivity.

These and other objects, features, and advantages of my invention will be apparent and a better understanding of my invention will be obtained from the following description taken in connection with the accompanying drawing in which,

Figure 1 is a plan view of one form of a foundation member suitable for use in practicing 5 my invention, I

Figure 2 is a greatly enlarged plan view of a portion of a mosaic electrode made in accordance with my invention, and

Figure 3 is a greatly enlarged cross-section -10 of a portion of the electrode shown in Figure 2.

Referring to Fig. 1 the mosaic electrode consists of a fine mesh wire screen with all of the wires coated with an enamel or other vitreous material having high electrical resistance. The usual enamels for ferrous metals may be used, although for use with a foundation material of nickel wire mesh I have found a vitreous enamel in which the percentages of alkali and of silica are considerably higher and thepercentage of 20 boric anhydrid is lower than in the usual enamels. Such an enamel as described by John L. Gallup in his co-pending application, Serial No. 115,192 filed September 10, 1936, is particularly advantageous because it is a poor solvent of 25 metals and has high electrical restivity. The particular screen shown comprises a frame I on which the insulated or enameled nickel screen 2 is held under slight tension. As best shown in Fig. 2, all of the nickel wire of the mesh is -30 covered with the enamel 3, so that the masses of metal or plugs 4 held in place in thescreen are thoroughly insulated from the screen by the enamel coating 3.

As best shown in Fig. 3, the nickel screen 2 of '35 foundation wires coated with the insulating enamel 3 has the interstices filled with a metal which diffuses very slightly into the enamel. and the plugs 4 have their exposed surfaces coated with caps 5 of another metal, which has higher 40 photoemissivity or secondary electron emissivity when treated with caesium or other alkali metal.

In accordance with my invention I fill the in" sulated interstices of the mosaic foundation with metals such as nickel, platinum, or palladium 45 which I have found dilfuse into the insulating enamel very slightly, and later I provide on the individual metal plugs filling the interstices a thin coating or cap 5 of metal such as silver which may be easily photosensitized or treated 50 to give high secondary electron emission when bombarded by high velocity electrons. Such a thin coating of silver has so little mechanical contact with the insulating coating that little or no silver difi'uses into the coating, and the re- 55 sistance between the plugs and the foundation is not reduced.

The nickel mesh foundation is a closely woven wire mesh screen and when such a screen is designed for use in television transmitting and receiving tubes it is desirable to provide a screen having 150-200 or more wires per linear inch if the tube is to be suitable for reproducing a. television image in good detail.

The nickel screen 2 is rolled and treated with acid to increase the area of the holes or interstices as described by Hickok in his patent referred to above. Prior to enameling the nickel mesh I find it advantageous to clean the nickel thoroughly, then oxidize it slightly by heating in air until it assumes a greenish color, probably due to a film of nickel monoxide, NiO. I then spray the mesh with the enamel ground to a particle size under two microns and held in suspension in either water or alcohol. The sprayed screen is then fired in a furnace at about 900 C., in air to fuse the enamel into a smooth glassy coating which completely covers all of the metal surface and adheres firmly to it. I prefer to build the enamel coating up to a thickness of approximately 3 mils on the surface of the electrode and to a thickness of -1 mil on the walls of the holes in the electrode by applying the enamel in several thin coats and firing the screen after each coat is applied. I find in this way that well-insulated screen electrodes highly suitablefor the production of mosaic electrodes for television transmitting or receiving tubes can be made with such a wire woven screen.

Following the formation of the insulating coating on the screen I fill the interstices thereof with a quantity of finely-ground nickel powder which is mixed with rosin oil diluted slightly with turpentine to make a semi-liquid paste which is brushed into the screen with a camels hair brush until the interstices are completely filled. The surface of the electrode may be cleaned by removing excess material with a cloth slightly moistened with acetone. This cleaning operation likewise removes excess material from the interstices leaving plugs which are slightly concave on their exposed surfaces. A metal powder suitable for this purpose is available on the market and is commercially known as 325 mesh nickel powder. Palladium and platinum powder suitable for the purpose may also be obtained on the market under the commercial name of Palladium powder and Platinum powder. This powder is sifted through a 400 mesh screen to remove any particles larger than 25 microns. The prepared screen is then baked in air for a period of approximately 15 minutes at ZOO-300 C., to drive off the rosin oil and turpentine, followed by another baking in air from one half to one hour at LOO-600 C., to sinter the metal powder and form a coherent mass. The sintering of the nickel powder provides a mosaic electrode which will withstand handling and normal mechanical shock during use without the metal plugs falling out of the interstices, and also reduces the electrical resistance of the plugs.

While an electrode made as above described is suitable as a mosaic electrode for use in television receiving and transmitting tubes, I find it advantageous to deposit on the exposed surfaces of the plugs l another metal which forms a better base for a photoelectrically sensitive electrode than the metal of the plugs. The use of a thin layer of silver on the plugs is advantageous for this reason, and also for obtaining uniform secondary emission from the plugs when bombarded by a high velocity electron beam. This silver layer may be subsequently photosensitized or treated to have the desired secondary electron emission properties during the exhaust operation of the tube in which the electrode is used. If nickel plugs are used any nickel oxide which may have been formed in the sintering operation should be reduced by heating the electrode in an atmosphere of hydrogen for a period of approximately three minutes at 100 C., before depositing on the nickel plugs 4 the thin layer 5 of silver. The metal layer 5 may be conveniently formed on the individual plugs 4 by an electro lytic deposition process, and for this use I have found a solution made up of the following constituents to be particularly suitable for this purpose.

Sodium cyanide oz 5 Silver cyanide oz 3 Sodium carbonate oz 5 Water "gal" 1 This solution is used as an electrolyte in which the mosaic electrode is suspended between a silver anode and a nickel cathode. I have used an electric current of 600 ma, for a period of 10 minutes to coat the metal plugs in a screen having an area of approximately 20 square inches and have found that such treatment produces a coating of silver sufficiently thick for optimum photosensitivity when oxidized and photosensitized with caesium or other alkali metal.

Mosaic electrodes made in accordance with my invention may be used for applications where it is desirable to have the exposed areas of the plugs on one side of the electrode photosensitizcd, the opposite side having little or no photosensitivity. For such applications it may be desirable to form the silver coating 5 on the exposed surfaces of the plugs 4 on only one side of the electrode, leaving the nickel plugs 4 exposed on the oposite side. In making an electrode of this type it is desirable to coat one side of the electrode with a film or layer of paraffine or other material which will prevent the deposition of silver on the exposed ends of the nickel plugs on that side of the electrode. If paraiiine is applied to one side of the electrode to prevent deposition of silver on the exposed surfaces of the plugs on that side, the parafline may be removed after the opposite side of the electrode is treated by baking the assembly in air at a temperature of IOU-200 C., for a period of approximately 15 minutes.

Mosaic electrodes made in accordance with my invention are particularly suitable for use in television transmitting and receiving tubes and may be sealed into the tube and photoelectrically sensitized by oxidizing the silver caps 5 and treating with caesium in the usual way. One method which has proven satisfactory is that disclosed by Sanford F. Essig in U. S. Patent 2,065,570, December 29, 1936.

It has been found that when silver is used for the plugs a small portion of the silver diffuses through the insulating enamel thereby forming between the silver plugs and the foundation member a path of low electrical resistance. However, with the use of nickel or other nondiffusing metal the electrical resistance of the plugs is low, probably due to grain growth of the metal, and the resistance between the plugs and the foundation member insulated with the enamel above recommended is extremely high,

being between 1X10 and 1x10 ohms, per square centimeter compared with a resistance of 1X10 and 1X 10 ohms per square centimeter for mosaic electrodes with silver plugs.

In addition to the high resistance between the individually insulated plugs and the foundation member I have found that electrodes made in accordance with myinvention have fewer contacts between the plugs and the foundation, which makes such electrodes particularly advantageous for use in cathode ray transmitting and receiving tubes where uniformity and fidelity of image transmission is desirable.

From the foregoing description it will be ap- 15 parent that various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire, there fore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claim.

I claim:

An electrode for electron discharge devices comprising a nickel base member having a plurality of apertures, an electrically insulating coating of vitreous enamel on the walls of said apertures, and conductive plugs within the apertures of said base member consisting of nickel,

whereby the electrical leakage through the enamel is a minimum.

ROBERT B. JANES. 

